Seasonality of floc strength in the southern North Sea
Fettweis, M.; Baeye, M.; Van der Zande, D.; Van den Eynde, D.; Lee, J (2014). Seasonality of floc strength in the southern North Sea. J. Geophys. Res. Oceans(119): 1911-1926. dx.doi.org/10.1002/2013JC009750
In: Journal of Geophysical Research. American Geophysical Union: Richmond. ISSN 0148-0227; e-ISSN 2156-2202, more
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suspended particulate sediments; flocculation; seasonal variation; algaebloom |
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- Van den Eynde, D., more
- Lee, J
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| Abstract |
The suspended particulate matter (SPM) concentration in the high turbidity zones of the southern North Sea is inversely correlated with chlorophyll (Chl) concentration. During winter, SPM concentration is high and Chl concentration is low and vice versa during summer. This seasonality has often been associated with the seasonal pattern in wind forcing. However, the decrease in SPM concentration corresponds well with the spring algal bloom. Does the decrease of SPM concentration caused by changing wind conditions cause the start of algae bloom, or does the algae bloom decrease SPM concentrations through enhanced flocculation and deposition? To answer the question, measurements from 2011 of particle size distribution (PSD), SPM, and Chl concentrations from the southern North Sea have been analyzed. The results indicate that the frequency of occurrence of macroflocs has a seasonal signal, while seasonality has little impact upon floc size. The data from a highly turbid coastal zone suggest that the maximum size of the macroflocs is controlled by turbulence and the available flocculation time during a tidal cycle, but the strength of the macroflocs is controlled by the availability of sticky organic substances associated with enhanced primary production during spring and summer. The results highlight the shift from mainly microflocs and flocculi in winter toward more muddy marine snow with larger amounts of macroflocs in spring and summer. The macroflocs will reduce the SPM concentrations in the turbidity maximum area as they settle faster. Consequently, the SPM concentration decreases and the light condition increases in the surface layer enhancing algae growth further. Key Points SPM and Chl concentration have opposing seasonal signal The seasonality of SPM concentration is mainly caused by biological effects Macroflocs are more abundant and stronger in summer than winter season |
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